Field
The disclosure relates to transformers for electronic circuitry.
Background
Wireless transceivers commonly incorporate circuitry for operating in a plurality of modes. For example, a radio-frequency (RF) receiver may include a first low-noise amplifier (LNA) for receiving a first frequency band, and a second low-noise amplifier for receiving a second frequency band. The outputs of the LNA's may each drive an inductive load, e.g., first and second primary windings, respectively, of a transformer, and the inductive loads may further be mutually coupled to a secondary winding of the transformer. The secondary winding may generate a differential signal for further processing by a down-conversion mixer, which may be shared between the two frequency bands.
In a typical implementation, if only one frequency band is processed at a time, the first LNA may be active when the second LNA is inactive. Even when the second LNA is inactive, however, the second primary winding is still mutually (magnetically) coupled to the secondary winding of the transformer. This mutual coupling may undesirably attenuate and/or add noise to the signal coupling between the first primary winding and the secondary winding when the first LNA is active. A similar phenomenon occurs when the second LNA is active and the first LNA is inactive. The additional attenuation and noise introduced by these effects degrade the performance of the multi-band transceiver.
It would be desirable to provide techniques for improving the performance of transformers accommodating multiple modes in wireless transceivers.